Acyclic monoolefin double-bond isomerization using a nonacidic supported nickel, iron or cobalt catalyst with either antimony or arsenic

ABSTRACT

A method and catalysts for isomerization which involves contacting a feedstream with hydrogen and with various supported catalysts of metallic arsenides and antimonides, with carbon monoxide being optionally introduced into the reaction as a modifier.

This is a divisional application of our copending application havingSer. No. 574,824, filed May 5, 1975 now U.S. Pat. No. 4,020,119, whichwas a divisional of application Ser. No. 390,799, filed Aug. 23, 1973,now U.S. Pat. No. 3,900,526, issued Aug. 19, 1975, which was a divisionof application Ser. No. 249,726, filed May 2, 1972, now U.S. Pat. No.3,787,511, issued Jan. 22, 1974, which was a division of Ser. No.44,665, filed June 8, 1970, now U.S. Pat. No. 3,697,448, which in turnwas a continuation-in-part application of Ser. No. 6,971, filed Jan. 29,1970, now abandoned.

This invention pertains to selective hydrogenation.

In one of its more specific aspects, this invention pertains to the useof reduced nickel arsenate on alumina catalyst for the selectivehydrogenation of diolefins to the corresponding monoolefins.

Various compounds of nickel are known as active and selectivehydrogenation catalysts for conversion of diolefins or monoolefins. Forextended use, compounds such as nickel sulfide require the continuousaddition of small amounts of sulfur to maintain catalyst activity. Suchaddition can create a sulfur removal problem when the selectivelyhydrogenated products are to be further processed in other catalyticreactors in which minute amounts of sulfur are detrimental.

There has now been discovered a selective hydrogenation catalyst whichdoes not require the presence of objectionable sulfur-containingauxiliary materials to maintain its selectivity. This catalyst can beemployed to selectively hydrogenate diolefins to monoolefins, to doublebond isomerize monoolefins in the presence of hydrogen and tohydrogenate reducible catalyst poisons such as sulfur, carbonyls,oxygen, and acetylenes in the presence of monoolefins.

According to the method of this invention, there is provided a processfor selectively hydrogenating polyenes to monoolefins, for isomerizingmonoolefins in the presence of hydrogen and for hydrotreating olefinicstreams containing minor amounts of materials such as compounds ofsulfur, carbonyls, oxygen, and acetylene which comprises contacting thestream comprising at least one of the aforementioned materials withhydrogen and with an after-described catalyst under reaction conditions.

According to this invention, the aforementioned contact is made with acatalyst comprised of a metal selected from the group consisting ofiron, cobalt, and nickel in the form of its arsenide or antimonidederivatives, or mixtures thereof.

Accordingly, it is an object of this invention to provide a simplyprepared catalyst which possesses sustained activity.

It is another object of this invention to provide a selectivehydrogenation process which is resistant to typical catalyst poisons andwhich can be used for sustained periods without requiring regeneration.

The method of this invention is broadly applicable to the selectivehydrogenation of olefinic feedstocks. The process is selective becauseit provides a method of hydrogenating materials such as acetyleniccompounds, organic sulfur compounds, organic peroxides, carbonylcompounds, cyclic and acyclic polyenes, and the like. However, theprocess is without substantial activity for the hydrogenation ofmonoolefins. In some instances, no hydrogenation of monoolefins isdetectable.

When applied to a cyclic or acyclic polyene, the process selectivelyhydrogenates these to cyclic or acyclic monoolefins with substantialselectivity depending upon the specific feeds, catalysts, and conditionsused. Similarly, feedstreams which contain substantial amounts ofmonoolefins can be effectively hydrotreated to hydrogenate minor amountsof impurities, e.g., acetylenes, dienes, sulfur compounds, withoutsignificant conversion of the monoolefins to saturates. Thus, theinvention is applicable for hydrogenating olefinic feedstocks wheremonoolefins are a substantial portion of the product. These productmonoolefins can be present in the feed, or can be produced within thereaction zone as a hydrogenation product from a more unsaturatedolefinic compound.

The olefinic feedstocks can be diluted with nonhydrogenatable or inertdiluents. Olefinic refinery streams can be used as feedstocks.

Applicable polyenes are those olefinic hydrocarbons which have more thanone double bond per molecule. For purposes of this invention, acetylenichydrocarbons are also included in this scope, because both acetylenesand dienes, for example, can be selectively hydrogenated to monoolefins.In general, any polyene, capable of being hydrogenated, can beselectively hydrogenated by the process of this invention. As a matterof practical commercial application, polyenes having up to about 15carbon atoms per molecule are preferred. Some examples of these areacetylene, 1,3-pentadiene, 1,5-cyclooctadiene, 1,3,7-octatriene,4-vinylcyclohexene, 1,4,9-decatriene, 1,5,9-cyclododecatriene, 2-hexyne,3,4-dimethyl-1,6-tridecadiene, and the like, and mixtures thereof.

Similarly, the monoolefins which can be subjected to the process of thepresent invention for hydrotreatment of impurities and/or double bondisomerization include any such cyclic or acyclic olefins which arenormally hydrogenatable. As a practical matter, monoolefins of up toabout 15 carbon atoms per molecule are of commercial importance and arepreferred. Some examples of these are ethylene, propylene, butene-1,pentene-1, heptene-2, 4-methylpentene-1, 3-ethylcyclohexene, decene-5,octene-1, 4-ethyl-6-tridecene, and the like, and mixtures thereof.

As mentioned, the catalysts are the arsenide or antimonide forms ofiron, cobalt, and nickel. In its preferred form, the catalyst of thisinvention is a supported, reduced nickel arsenide. Such nickel-arseniccombinations as are satisfactory have the empirical formula NiAs_(x), inwhich x can have a value from about 0.33 to about 2.0, preferably 0.6 to1.0, and includes nickel arsenide compounds such as NiAs, NiAs₂, and Ni₃As₂. However, the proportions of nickel and arsenic need not bestoichiometric; an excess of either the nickel or the arsenic can bepresent.

If the nickel is employed in its antimonide form, the combination willhave the empirical formula NiSb_(x), in which x can have a value of fromabout 0.33 to about 2.0, preferably 0.6 to 1.0. Suitable forms are NiSb,NiSb₂, Ni₃ Sb, Ni₅ Sb₂, Ni₇ Sb₃, Ni₂ Sb₃, and Ni₃ Sb₅. The proportionsof nickel and antimony need not be stoichiometric. Generally, the nickelis employed in the form of NiY_(x) in which Y is arsenic or antimony andx has a value from about 0.33 to about 2.0, preferably about 0.6 toabout 1.0.

If cobalt and iron are substituted for nickel, the same empiricalformula applies.

Generally then, the catalysts of this invention have the formula MY_(x)in which M is a metal selected from the group consisting of nickel,cobalt and iron, Y is arsenic or antimony and x has a value from about0.33 to about 2.0, preferably about 0.6 to about 1.0. Because of itsgreater selectivity, Y is preferably arsenic.

For purposes of this disclosure, the invention will be most frequentlyexplained in terms of the nickel arsenide catalyst without meaning tolimit the invention thereto. All uses and applications of any one of thecatalysts specifically designated are intended to apply to all of thecatalysts which are the subject of this invention.

While a supported type catalyst is preferred, the catalyst can also beemployed in a nonsupported state as, for example, in the form in whichthe principal components are coprecipitated from a sol.

In its supported state, any conventionally employed nonacidic orrelatively nonacidic catalyst support can be used. Preferable supportsinclude gamma-alumina, alpha-alumina, silica, magnesia, charcoal,calcium aluminate, natural or synthetic molecular sieves and theircombinations. In general, the granular support will have a surface areaof about 1 to about 400 square meters per gram.

In the preparation of the catalysts, the nickel and arsenic, orantimony, can be simultaneously deposited on the support as, forexample, by precipitating nickel arsenate or nickel antimonate on thesupport; or the support can be impregnated with the nickel and thearsenic, or antimony, in individual treatments. In either instance,sufficient nickel is employed to deposit about 0.1 to about 20,preferably from about 0.5 to about 10, weight percent nickel on thesupport and sufficient arsenic or antimony is employed so as to producea finished catalyst containing from about 0.05 to about 50 weightpercent, preferably 1.0 to 10 weight percent, arsenic or antimony.

Thus, the catalyst can be prepared by impregnation of a suitablecatalyst support with a water soluble salt, such as a nitrate, halide,etc. of nickel, cobalt, or iron. The impregnated support can then becalcined and re-impregnated with an aqueous solution of, for example,ammonium arsenate prepared by dissolving arsenic trioxide inammonia-water.

Under any method of preparation the base, after deposition thereon ofthe materials concerned, can be washed to remove undesirable solublesalts, dried, calcined in air, and then reduced with hydrogen at anysuitable temperature and pressure which is sufficient to produce theactive nickel arsenide or antimonide. For example, hydrogen reduction atatmospheric pressure at 500° to 800° F for 0.1 to 20 hours can be used.In some instances, the calcination in air step can be omitted.

The catalysts of the present invention have no appreciable skeletalisomerization ability; that is, when contacted with straight chainmonoolefins or polyenes under the reaction conditions specified, theypromote little branching of the molecule. Since the skeletalisomerization ability of a supported catalyst is generally a function ofits acidity, which is largely contributed by the support, the use ofacidic supports which promote skeletal isomerization is to be avoidedand nonacidic supports are preferred. This is due to the fact that suchacidic supports do not give the selective hydrogenation results of thepresent invention. However, some mildly acidic supports, such as theflame-hydrolyzed aluminas, are satisfactory for use in the presentinvention if their acidic character is minimized or destroyed during thecatalyst preparation. Accordingly, ammoniacal solutions or basicprecipitants are preferentially employed in preparing the catalystssince the former act to reduce the acidity of the support, to avoidskeletal isomerization activity, and to provide a selectivehydrogenation catalyst.

The conditions under which the method of this invention is employed,whether for selective hydrogenation or poison removal by hydrogenation,can vary widely. Generally, the reactions are conducted by passing thehydrocarbon stream, as a vapor, with hydrogen into contact withcatalyst, the reaction zone being maintained at a temperature of fromabout 75° F to about 750° F, preferably from about 200° F to about 600°F, at a pressure of from about atmospheric to about 1,000 psig. Thehydrocarbon stream is passed in contact with the catalyst at a ratesufficient to provide a liquid hourly space velocity (LHSV) of fromabout 0.1 to about 10. Hydrogen is introduced at a rate which provides ahydrogen to feed molar ratio of from about 0.1 to 1 to about 5 to 1.

The selectivity of the process and catalyst of this invention can beimproved by incorporating carbon monoxide in the feedstock. Carbonmonoxide in amounts of about 50-100,000 ppm, preferably from about 500to about 5,000 ppm, of the feedstream have been found to be effective.The carbon monoxide can be introduced with the feedstock, with hydrogenor it can be separately introduced.

The catalysts of this invention can be regenerated in a number of waysincluding conventional calcination in diluted air. Inasmuch as thereaction conditions to which these catalysts are subjected arerelatively mild, catalyst regeneration can be primarily directed to theremoval of viscous oil deposits. Accordingly, the catalysts can beregenerated by removing these deposits by oxidation or by washing with aliquid aromatic solvent under conditions suitable for removing thedeposits. Preferably, benzene, toluene, xylene, and mixtures thereof arepassed through the catalyst bed at a temperature such as 200°-250° F,the bed being thereafter flushed with warm hydrogen or an inert gas.

The catalysts of the present invention, particularly in the nickelarsenide form, are suitable under the reaction conditions previously setforth, for the double bond isomerization of monoolefins. Best resultsare obtained at 350°-600° F, preferably at 400°-500° F. In thisapplication, nonacidic supports are employed. An amount of hydrogensufficient to keep the catalyst unimpaired, or clean, is employed.Carbon monoxide can also be included in the feed.

The following examples indicate methods of preparing the catalysts ofthis invention and their employment in the method of this invention.

EXAMPLE I

A nickel arsenide catalyst was prepared by impregnating a catalyticgrade alumina gel base with sufficient nickel sulfate to provide 4.25weight percent nickel based on the weight of the alumina. Thenickel-impregnated alumina was then impregnated with a stoichiometricamount of sodium arsenate. The impregnated base was then washed toremove soluble salts, dried and reduced with hydrogen at atmosphericpressure and at a temperature of about 520° to 600° F for 11/2 hours toform the catalyst, which contained a nominal Ni₃ As₂ composition.

EXAMPLE II

A nickel arsenide catalyst was prepared as follows: 98.5 grams of nickelnitrate, Ni(NO₃)₂.6H₂ O, were dissolved in 1200 ml of distilled waterand 150 g of finely divided, flame-hydrolyzed alumina were added to thesolution to produce a slurry. To this slurry, 32.1 grams of arsenicacid, H₃ AsO₄, dissolved in 300 ml of distilled water were added. Theresulting slurry was neutralized with ammonium hydroxide to a pH of 7.

The mixture was filtered and the solids were washed with distilledwater, refiltered, dried, and heated to 1000° F at which temperaturethey were maintained for 2 hours. The solids were then ground andscreened and 95 grams of a 9 to 20 mesh catalyst were recovered. Thiscatalyst contained 9.8 percent nickel, 9.1 percent arsenic, had asurface area of 70 m² /gm and a pore volume of 0.63 cc/gm. Before use,the catalyst is reduced in the presence of hydrogen at 520° to 600° F.

EXAMPLE III

A charcoal-based catalyst was prepared by impregnating 6/14 mesh coconutcharcoal with a nickel acetate solution. The impregnated charcoal wasdried at 250° F and impregnated with H₃ AsO₄, dried at 250° F and washedwith aqueous ammonia. Activation was accomplished by heating at 800° Fin hydrogen for two hours, the air calcination step being omitted. Thecatalyst is active for selective hydrogenation of polyenes.

EXAMPLE IV

Due to the low solubility of most antimony compounds, differenttechniques were used to make the antimony-containing catalysts. Onesuitable method was to dissolve antimony trioxide (Sb₂ O₃) in a watersolution of tartaric acid containing a small amount of nitric acid. Thisstep formed an antimonyl tartrate compound. The required amount ofnickel acetate or nickel nitrate was then dissolved in the tartratesolution to form a clear green solution containing both nickel andantimony. This solution was then used to impregnate the preformedcatalyst base pellets, which were dried, and then calcined in air at900° to 1000° F to remove the organic portion of the impregnatingcompound. The calcined catalyst was then heated in a stream of hydrogenat 500° to 900° F, after which it was ready to use.

Similar methods to the above have been employed to support bothnickel-arsenide and nickel-antimonide on magnesia, silica, Celite, andcalcium aluminate (CaAl₂ O₄) supports, the resulting catalysts in allinstances being effective for selective hydrogenation.

EXAMPLE V

The catalyst prepared in Example I was employed for the selectivehydrogenation of a stream comprised of substantial amounts of4-vinylcyclohexene in cyclohexane diluent. The conditions under whichthe run was conducted, and the selective hydrogenation effected, areindicated by the following:

    ______________________________________                                                             Product From Selective                                                        Hydrogenation with                                                            Nickel Arsenide on                                       Stream               Alumina (4.25% Ni)                                       ______________________________________                                        Operating Conditions                                                          Temperature, ° F                                                                           534                                                       Pressure, psig      100                                                       Liquid Hourly Space Velocity (LHSV)                                                               2                                                         Product Analysis, Wt. % (Diluent Free)                                        Ethylcyclohexane    10.7                                                      1-Ethylcyclohexene  51.6                                                      4-Ethylcyclohexene  5.9                                                       3-Ethylcyclohexene  15.7                                                      Ethylbenzene        12.2                                                      4-Vinylcyclohexene  0                                                         Ethylidenecyclohexane                                                                             3.9                                                       ______________________________________                                    

These data indicate that the catalyst and method of this invention areeffective in selectively hydrogenating 4-vinylcyclohexene to primarilymonoolefinic compounds.

EXAMPLE VI

The following illustrates the effectiveness of the method and catalystof this invention in hydrotreating a stream of mixed monoolefins. Thismixture of polymerized lower olefins (cat poly-gasoline) was used as afeedstock to an olefin disproportionation reaction to produceisoamylenes for isoprene manufacture. This stream was hydrogenated forthe purpose of reducing the concentrations of certain undesirablematerials such as sulfur compounds and carbonyl compounds such asaldehydes and ketones. Operating conditions and results are presentedwhen employing a nickel arsenide catalyst similar to that prepared inExample I.

    ______________________________________                                        Operating Conditions                                                          Temperature, ° F     475                                               Hydrogen Pressure, psig     100                                               Liquid Hourly Space Velocity                                                                              2.7                                               Stream          Feed        Product                                           ______________________________________                                        Carbonyls, ppm  115         2                                                 Sulfur, ppm     7           5                                                 Saturates, wt. %                                                                              3.3         3.7                                               Maleic Anhydride Value                                                                        5.2         4.6                                               ______________________________________                                    

The above data illustrate that the method and catalyst of this inventionreduced the sulfur, conjugated diene and carbonyl concentration of thehighly olefinic feedstream without significant increase in saturates.

EXAMPLE VII

The following example illustrates the results of hydrotreating a heptenefeed stream with the catalyst and by the method of this invention. Thisheptene stream and an IBP of 181° F, and EP of 251° F, and contained24.9 percent cycloolefins and straight chain diolefins, 3.1 percentcyclodiolefins and 35.6 percent monoolefins. It was hydrotreated withthe catalyst prepared in Example I for diolefin conversion tomonoolefins and for sulfur reduction. Feedstream analysis, operatingconditions and product stream analyses were as follows:

    ______________________________________                                        Operating Conditions                                                          Temperature, ° F     510                                               Hydrogen Pressure, psig     100                                               Liquid Hourly Space Velocity                                                                              2.5                                               Stream          Feed        Product                                           ______________________________________                                        Sulfur, ppm     253         95                                                Maleic Anhydride Value                                                                        28.7        6.0                                               Saturates, Wt. %                                                                              28.2        29.3                                              ______________________________________                                    

These data indicate a significant reduction in sulfur content and indiolefin content. The increase in saturate content is nonsignificantsince the values are within the accuracy of the test method employed.

EXAMPLE VIII

The method and catalyst of this invention are effective for selectivehydrogenation of 1,5-cyclooctadiene to cyclooctene as shown by thefollowing series of runs in which cyclooctadiene was passed withhydrogen over a catalyst comprising 8.6 weight percent nickel and 8.6weight percent arsenic on an alumina base.

The nickel arsenide catalyst was 20/40 mesh and had a surface area of 83m² /g and a pore volume of 0.73 ml/g. In all instances, carbon monoxidewas introduced into the reaction and had the effect, as previouslymentioned, of modifying the extent to which the selective hydrogenationtook place.

    ______________________________________                                        Run No.         I      II    III  IV    V   VI                                ______________________________________                                        Catalyst, Quantity, gms                                                                      13.9   13.9   13.9 13.9 13.9 13.9                              Reaction Pressure, psig                                                                      100    100    200  200  300  300                               Reaction Temperature, 20  F                                                                  360    360    360  360  360  360                               Feed Rate, mols/hr.                                                           Hydrogen       0.954  0.448  1.10 0.563                                                                              1.050                                                                              1.080                             Carbon Monoxide                                                                              0.046  0.022  0.053                                                                              0.027                                                                              0.052                                                                              0.053                             Cyclohexane    0.599  0.602  0.569                                                                              0.255                                                                              0.251                                                                              0.602                             1,5-Cyclooctadiene                                                                           0.052  0.053  0.049                                                                              0.018                                                                              0.022                                                                              0.052                             C.sub.8 Product                                                               Distribution, %                                                               Cyclooctane    1.25   1.09   2.39 7.10 8.64 2.94                              Cyclooctene    97.60  97.68  97.60                                                                              92.89                                                                              91.36                                                                              97.06                             1,3-Cyclooctadiene                                                                           1.13   1.19   0.01 0.01 <.01 <.01                              1,4-Cyclooctadiene                                                                           0.07   0.03   <.01 <.01 <.01 <.01                              1,5-Cyclooctadiene                                                                           0.06   0.01   <.01 <.01 <.01 21 .01                            ______________________________________                                    

These data illustrate that the invention catalyst inhibited with carbonmonoxide shows excellent selectivity and that it is possible to reducediolefin content to less than 0.05 percent and maintain excellentselectivity to cyclooctene. Under these conditions in the absence of COconversion of cyclooctadiene to cyclooctane was typically 18-20 percent.

The selective hydrogenation of cyclooctadiene, as shown above, has beeneffectively carried out in runs of up to 80 hours in duration. Thisdemonstrates the highly desirable long-lived characteristic of thiscatalyst system and process.

The effect of the addition of carbon monoxide is also shown in theemployment of the method and catalyst of this invention for theselective hydrogenation of acetylene.

EXAMPLE IX

The following runs, in which streams containing acetylene and ethylenewere hydrogenated with, and without, the presence of carbon monoxide,were conducted employing a nickel arsenide agent on alumina, thequantities of nickel and arsenic being 8.3 and 7.6 weight percent of thetotal catalyst, respectively. The runs were made under comparableconditions, the carbon monoxide being introduced into the reactor as agas with the feed in both instances. Results were as follows:

    ______________________________________                                        Run No.         I          II                                                 ______________________________________                                        Carbon Monoxide Introduced                                                                    yes        No                                                 Reaction Conditions                                                           Pressure, psig  365        365                                                Temperature, ° F                                                                       230, steady                                                                              230 - rising to                                                               520 in 11/2 hours                                  Gaseous Hourly Space Velocity                                                                 5000       5000                                               Feed Analysis, Vol. %                                                         Hydrogen        80         80                                                 Ethylene        20         20                                                 Acetylene, ppm  540        540                                                Carbon Monoxide (ppm)                                                                         540        0                                                  Product Analysis*                                                             Acetylene       <1 ppm     <1 ppm                                             Ethane, wt. %   0.2        30% after 20                                                                  minutes reaction                                                              time                                               ______________________________________                                         *Hydrocarbon basis.                                                      

The results indicate that the addition of carbon monoxide improves theselectivity of the method and the catalyst for the hydrogenation ofacetylene in preference to ethylene. In the absence of CO, more ethylenewas destroyed as evidenced by the analysis and the temperature rise.

In other runs the use of carbon monoxide has been found to producesimilar results with the other catalysts of this invention. This hasbeen particularly true of nickel arsenide on alumina for selectivelyhydrogenating acetylene in ethylene during operating periods of up to600 hours.

The introduction of carbon monoxide into the reaction zone is alsoeffective in improving the selectivity when hydrogenating diolefins tomonoolefins in respect to minimizing the extent of monoolefinhydrogenation. This is illustrated by the following example involvingthe selective hydrogenation of 1,5-cyclooctadiene to cyclooctene atvarious levels of carbon monoxide concentration in the reaction zone.

EXAMPLE X

Each of the following hydrogenations was conducted in the presence of 10g. of an alumina-supported nickel arsenide catalyst containing 8.3weight percent nickel and 7.6 weight percent arsenic. The feedstreamcomprises 1,5-cyclooctadiene in n-pentane diluent, hydrogen, and carbonmonoxide. The 1,5-cyclooctadiene comprised 6.6 mole percent of the totalhydrocarbon in the reaction mixture. The concentration of carbonmonoxide in relation to the moles of 1,5-cyclooctadiene was the onlysignificant factor varied. Results were as follows:

    __________________________________________________________________________    Reac-    Reac-                                                                              Mols, 1,5-     Hydro-                                                                              Product Distribution                       tor      tor  Cycloocta-                                                                            Hydrogen                                                                             carbon                                                                              Wt. %                                      Run Temp.,                                                                             Press.,                                                                            diene per                                                                             Moles  Moles Cyclooctadiene                                                                            Cyclo-                                                                             Cyclo-                    No. ° F.                                                                        psig Mole of CO                                                                            per Hour                                                                             per Hour                                                                            1.5 1.4 1.3                                                                             octene octane                    __________________________________________________________________________    1   400  100  7.0     0.94   0.415 18.9                                                                              14.7                                                                              35.8                                                                              28.0 2.5                       2   400  200  7.0     0.74   0.36  11.2                                                                              11.5                                                                              33.8                                                                              40.8 2.7                       3   400  400  7.0     0.79   0.420 1.2 0.7 3.1 90.6 4.5                       4   400  400  3.5     0.81   0.268 0.4 0.4 4.1 92.0 3.0                       5   430  400  3.5     1.06   0.296 0.2 0.1 0.4 92.7 6.7                       __________________________________________________________________________

These data show that carbon monoxide prevents runaway conversion tocyclooctane and illustrate an increasing selectivity in the conversionof the cyclooctadiene to cyclooctene with an increase in carbon monoxideto 1,5-cyclooctadiene ratio. This is particularly evident at higherreactor pressures as shown by comparison of Run 3 with Run 4.

The selective hydrogenation of cyclooctadiene has been carried out withthe various catalysts of this invention in runs of up to 80 hours induration.

As mentioned, the method and catalysts of this invention are alsosuitable for the double bond isomerization of monoolefins. The followingis illustrative of this.

EXAMPLE XI

A catalyst comprising nickel arsenide on alumina, prepared in accordancewith one of the previously described methods, was contacted with amixture comprising 10 percent pentene-1 and 90 percent cyclohexane atthe rate of 3.1 volumes of feed per hour per volume of catalyst.Hydrogen and carbon monoxide were introduced into the reaction zone, asa mixture containing 2 percent carbon monoxide in hydrogen, at a rate of600 volumes of the mixture per hour per volume of catalyst. Initialreaction conditions were 375° F and 100 psig. Under these conditions, 15percent of the pentene-1 was converted to cis- and trans-pentene-2isomers.

The reaction conditions were then altered to 475° F and 200 psig, underwhich conditions an equilibrium mixture of double bond isomers ofpentene was produced, at which point the reaction mixture was comprisedof about one part pentene-1, about three parts cis-pentene-2 and aboutsix parts trans-pentene-2. Only two percent of the original pentene hadbeen hydrogenated to pentane.

In the double bond isomerization of monoolefins as described above, thepresence of carbon monoxide has also been found effective in limitingthe extent to which hydrogenation takes place. Further, because of itsrelative insensitivity to typical catalyst poisons, such a process iscapable of long operating periods between regenerations.

One acceptable procedure for regenerating the catalyst by solventwashing is described in the following.

EXAMPLE XII

A bed of contaminated nickel arsenide on alumina catalyst, which hadbecome spent in the selective hydrogenation of acetylenes in ethylene inaccordance with the method of this invention, was washed with tolueneand a viscous residue amounting to about 18 percent of the catalyst waswashed from it. The catalyst was then blown substantially dry with warmflue gas and returned to service. The results of the hydrogenation usingthe washed catalyst were as follows:

    ______________________________________                                                          Spent Catalyst                                                                After Regeneration By                                                         Extraction                                                  ______________________________________                                        Feed Rate, Hourly Space Velocity                                                                  6000                                                      Operating Temperature, ° F                                                                 230                                                       Operating Pressure, psig                                                                          350                                                       Feed Analysis, Mole %                                                         Hydrogen            77.8                                                      Ethylene            22.1                                                      Acetylene           0.078                                                     Carbon Monoxide     0.073                                                     Product Analysis, Mole %                                                      Acetylene, ppm      7                                                         Ethane, mole %      0.21                                                      Conversion                                                                    Acetylene, Mole %   99.1                                                      Ethylene to Ethane, Mole %                                                                        0.95                                                      ______________________________________                                    

These data indicate the effectiveness of the extraction method ofcatalyst regeneration employable with the method and catalyst of thisinvention in restoring the selective hydrogenation ability of thecatalyst.

Prior to its restoration by solvent washing, the spent catalyst hadlittle or no activity at 230° F. When the temperature was increased toimprove the activity, a runaway reaction occured with an uncontrollabletemperature increase up to about 440° F. About 50 percent of theethylene was then being converted to ethane.

EXAMPLE XIII

Cyclododecatriene was selectively hydrogenated to cyclododecene over arelatively low surface area alumina-supported nickel arsenide catalyst.The catalyst contained 9.0 weight percent nickel, 9.7 weight percentarsenic and had a surface area of 14.8 m² /g. A 10 weight percentmixture of cyclododecatriene in cyclohexane diluent was hydrogenatedduring passage through a fixed bed of this catalyst. The temperature was410° F, the pressure was 100 psig, and the feed rates for thecyclododecatriene, hydrogen and carbon monoxide were 8.09 × 10⁻⁴, 3.61 ×10⁻², and 7.4 × 10⁻⁴ moles per hour-gram of catalyst, respectively. Theresults of the run are shown by the analysis of the C₁₂ compounds in theeffluent:

    ______________________________________                                        C.sub.12 Product   Wt. %                                                      ______________________________________                                        Cyclododecene      85.4                                                       Cyclododecane      10.1                                                       Bicyclics          4.5                                                        Cyclododecatriene  0.0                                                        ______________________________________                                    

These data illustrate that the cyclododecatriene was completelyconverted. Also, they indicate that the cyclic triene was veryselectively converted to the cyclic monoolefin with little completehydrogenation of the cyclic triene to the saturated compound and withonly a minor amount of bicyclic formation.

It has been found that iron arsenides are particularly effective inconverting acetylenes to monoolefins or to polymers in the presence ofdiolefins with substantially no conversion of the diolefins themselves.Similarly, iron arsenides are effective in converting acetylenes tomonoolefins in the presence of diolefins and monoolefins withoutsubstantial conversion of either the diolefin or monoolefin.

The iron arsenide catalysts can be prepared in a number of ways whichembody the same general principles embodied in the preparation of thenickel catalyst. That is, the iron and arsenic, or antimony, can besimultaneously deposited on the support by precipitation or the supportcan be impregnated with iron and arsenic or antimony from suitablesolutions. In any instance, the ferric or ferrous iron is employed todeposit about 0.1 to about 20, preferably from about 0.5 to about 10,weight percent iron on the support and sufficient arsenic or antimony isemployed so as to produce a finished catalyst containing from about 0.05to about 50 weight percent, preferably 1.0 to 10 weight percent, arsenicor antimony.

The following methods of preparation are illustrative of but two ofthese.

In one preparation of iron arsenide catalysts, 104 g of a pilledcommercial gamma-alumina catalyst were immersed in an aqueous solutionof ferric nitrate and arsenic acid, prepared by dissolving 15 g ofFe(NO₃)₃.9H₂ O and 6 g of H₃ AsO₄ in 150 ml of deionized water. Aftertwo hours of contact, the pills were then calcined in air at 1000° F for4 hours after which they were contacted with hydrogen at 800° F for 4hours to reduce the ferric arsenate to iron arsenide.

In another preparation of the iron arsenide catalyst, 6 g of H₃ AsO₄were dissolved in 150 ml of water. Seventeen and six-tenths grams (17.6g) of FeSO₄.7H₂ O were dissolved in 150 ml of water. The two solutionswere combined and 50 g of Alon-C alumina were mixed with the solution.Ammonia was added to the mixture until the mixture had a pH of 8. Atthis pH, the ferrous arsenate precipitated out and the precipitatedferrous arsenate and Alon-C alumina were separated from the liquid anddried. The solids were then calcined in air at 1000° F for 1 hour afterwhich they were contacted with hydrogen at 800° F for about 16 hours toreduce the ferrous arsenate to iron arsenide.

Conversions employing the aforementioned iron catalysts were conductedusing a refinery-produced butadiene concentrate with both catalysts. TheC₄ fraction of this concentrate had the following composition by gasliquid chromatography:

    ______________________________________                                                          Mole %,                                                     Component         C.sub.4 Basis                                               ______________________________________                                        n-Butane          34.65                                                       1-Butene & Isobutene                                                                            12.56                                                       t-2-Butene        3.54                                                        c-2-Butene        2.83                                                        1,3-Butadiene     45.62                                                       1,2-Butadiene     0.17                                                        1-Butyne          0.08                                                        Vinylacetylene    0.54                                                        2-Butyne          0.01                                                                          100.00                                                      ______________________________________                                    

In the employment of the iron arsenide catalyst prepared from ferricarsenate, according to the method of this invention, the reaction wasconducted at 250° F and 500 psig at a butadiene concentrate WHSV of 0.6and a hydrogen GHSV of 560. Analysis of the product was as follows:

    ______________________________________                                                          Mole Percent,                                               Component         C.sub.4 Basis                                               ______________________________________                                        n-Butane          35.41                                                       1-Butene & Isobutene                                                                            12.07                                                       t-Butene-2        2.11                                                        c-Butene-2        3.29                                                        1,3-Butadiene     47.12                                                       1,2-Butadiene     --                                                          1-Butyne          --                                                          Vinylacetylene    --                                                          2-Butyne          --                                                                            100.00                                                      ______________________________________                                    

These data indicate that all of the C₄ acetylenes and all of the1,2-butadiene had been hydrogenated with no loss of 1,3-butadiene.

In the employment of the iron arsenide catalyst prepared from ferrousarsenate, according to the method of this invention, the reaction wasconducted at 315° F and 600 psig at a butadiene concentrate WHSV of 2.0and a hydrogen GHSV of 500. Analysis of the product was as follows:

    ______________________________________                                                          Mole Percent,                                               Component         C.sub.4 Basis                                               ______________________________________                                        n-C.sub.4 H.sub.10                                                                              38.00                                                       Butene-1 & Isobutene                                                                            13.50                                                       t-Butene-2        3.71                                                        c-Butene-2        3.47                                                        1,3-Butadiene     41.09                                                       1,2-Butadiene     0.19                                                        1-Butyne          0.03                                                        Vinylacetylene    0.00                                                        2-butyne          0.01                                                                          100.00                                                      ______________________________________                                    

These data indicate that all of the vinylacetylene had been hydrogenatedwith a 12 percent loss of 1,3-butadiene by hydrogenation.

It will be noted that the method of this invention employing theiron-containing catalysts can be carried out at somewhat lowertemperatures than those temperatures previously defined for the nickelcatalysts converting diolefins to monomers, that is, at temperaturesfrom about 200° F to about 400° F.

The aforementioned butadiene concentrate was contacted with a nickelarsenide catalyst and hydrogen for the purpose of carrying out thoseconversions conducted with the iron arsenides. This nickel arsenidecatalyst had been prepared by dissolving 98.5 g Ni(NO₃)₂.6H₂ O in 1200ml of water to which were added 150 g Alon-C alumina to make a slurry.To the slurry were added 32.1 g H₃ AsO₄ in 300 ml H₂ O giving a slurryof pH 1.6. Ammonium hydroxide was added until pH 7 when Ni₃ (AsO₄)₂precipitated. The slurry was then filtered, washed with water andfiltered again. The slurry was then heated 16 hours at 212° F; thecatalyst was calcined at 1000° F for 30 minutes after which it wascooled, ground and sieved to 10/20 mesh. The catalyst had an arseniccontent of 8.6 weight percent, a surface area of 83 m² /gm and a porevolume of 0.73 ml/g.

In a first run conducted at 200 psig, 218° F, a butadiene concentratefeed rate of 1.4 WHSV and a hydrogen feed rate of about 600 GHSV, all ofthe acetylenes and all but a trace of 1,2-butadiene were hydrogenated.However, about twelve percent of the 1,3-butadiene was alsohydrogenated.

It will be evident from the foregoing that various modifications can bemade to the method of this invention. However, such are considered asbeing within the scope of the invention.

We claim:
 1. A method for the double bond isomerizatin of acyclicmonoolefins without substantial hydrogenation of monoolefins whichcomprises contacting a feedstream containing acyclic monoolefins withhydrogen and a catalyst comprising a nonacidic support and a metalselected from the group consisting of nickel, iron, and cobalt and amaterial selected from the group consisting of antimony and arsenicunder conditions including temperature, pressure, and contact timesufficient to cause the double bond isomerization of said acylicmonoolefins without significant hydrogenation of said monolefins tosaturates, said catalyst being in a reduced state.
 2. A method accordingto claim 1 wherein said contacting is effected at a temperature in therange 350°-600° F with a nickel arsenidealumina catalyst.
 3. A methodaccording to claim 2 wherein pentene-1 is isomerized to cis- andtrans-pentene-2-isomers.
 4. A method as claimed in claim 1 wherein thecatalyst has the empirical formula MY_(x) in which M is a metal selectedfrom the group consisting of nickel, cobalt, and iron, Y is arsenic orantimony and x has a value from about 0.33 to about
 2. 5. A method asclaimed in claim 4 wherein x has a value from about 0.6 to about 1.0. 6.A method as claimed in claim 4 wherein said catalyst is on a nonacidicsupport selected from gamma-alumina, alpha-alumina, silica, magnesia,charcoal, calcium aluminate, natural or synthetic molecular sieves andtheir combinations.
 7. A method as claimed in claim 4 wherein saidcontacting is carried in the presence of carbon monoxide.
 8. A methodaccording to claim 7 wherein the amount of carbon monoxide presentranges from about 50-100,000 ppm of the feedstream, the temperature ofcontacting ranges from about 400°-500° F, and the catalyst is nickelarsenide-alumina.